An ordinary magnetic disk drive has a structure in which a single or a plurality of magnetic disks are disposed coaxially and driven by spindle motor. Reading or writing of information from or to the magnetic disk is performed by a magnetic head opposed to the magnetic disk. The magnetic head is supported by an arm and is driven by an actuator, thereby being able to access to respective tracks on the magnetic disk.
In general, performance required of a magnetic disk drive is measured by a storage capacity and a speed of reading or writing information, and various techniques are employed to improve the performance. The improved performance of the storage capacity can be achieved by increasing an information storage capacity per magnetic disk. Moreover, the improved performance of the speed of the reading or writing information can be achieved by increasing the number of revolutions of a magnetic disk to reduce time required to read and write information.
As described above, the techniques for improving the performance of the magnetic disk drive are employed, and factors responsible for determining the success or failure of these techniques include the positioning error of a magnetic head. The positioning error of a magnetic head means a relative position deviation between a target track and a magnetic head. When this positioning error is reduced, a track width can be also reduced and hence a higher-density large-capacity magnetic disk drive can be designed.
When the number of revolutions of a disk is simply increased to increase the speed of reading or writing information, the turbulence of an air flow caused by the rotation of the magnetic disk becomes larger, and hence causes an increase in the vibrations of an arm supporting the magnetic head and an increase in disk flutter that is the vibration of the magnetic disk itself. As a result, this makes the positioning error of the magnetic head worse, and hence makes it difficult to improve or maintain a recording density.
Thus, there is a tradeoff relationship between the narrowing of a track width to improve a recoding density, and the increasing of the number of revolutions of a disk to improve the speed of reading or writing information. To improve the performance required for magnetic disk drive, it is necessary to take some countermeasures to solve the tradeoff relationship.
In the number of revolutions of a disk of the present 3.5-type magnetic disk drive, 7,200 min−1 becomes predominant for a desktop and 10,000 to 15,000 min−1 becomes predominant for a server, respectively. Moreover, the storage capacity becomes approximately 500 Gbyte at the maximum. Required performances are an improved storage capacity and an improved speed of reading or writing information. However, against a backdrop such that multimedia becomes widespread and rapidly increases the quantity of information in the present product market, an improvement in the storage capacity becomes an important performance evaluation indicator of a product.
One way to improve storage capacity, that is, for increasing a storage capacity, is a method for narrowing a track width to increase a density. This requires reducing the positioning error of the magnetic head.
The main factor of the positioning error of the magnetic head, as described above, is a fluid force caused by the turbulence of air flow developed by the rotation of the magnetic disk. Conventional methods for reducing a fluid force include a method of disposing a straightening plate called a spoiler near the magnetic head. This straightening plate produces an effect of suppressing a flow directly hitting on the magnetic head or the arm to suppress the varying force of fluid applied to the magnetic head of the arm.
Here, patent documents relating to this spoiler include, for example, Japanese Patent Publication No. 6-84313 (“patent document 1”) and Japanese Patent Publication No. 2004-234784 (“patent document 2”).
Moreover, a technique for suppressing the vibrations of an actuator arm caused by the turbulence to provide a magnetic disk drive of high positioning accuracy is disclosed in Japanese Patent Publication No. 2004-171713 (“patent document 3”). In this magnetic disk drive, against a whirling air flow flowing on a disk surface along with the high rotation speed of the disk, there are provided a branch flow passage bypassing an actuator and two spoilers for introducing the air flow into the branch flow passage, the two spoilers being disposed on the upstream and downstream portions of the actuator arm. With this, the magnetic disk drive makes the most part of the whirling air flow bypass the actuator into the branch flow passage to reduce an air flow rate to the actuator arm.
However, in order to realize a larger-capacity magnetic disk drive, a structure is required that produces an effect larger than an effect produced by the spoiler shown in the patent documents 1 and 2.
Moreover, the magnetic disk drive shown in patent document 3 has a complicated structure requiring the branch flow passage and hence raises a problem of upsizing a disk drive and increasing manufacturing cost.